WASHINGTON — Democratic U.S. senators and environmental groups blasted plans they believe may be in the works to roll back tough fuel-use standards for vehicles.

They argue that a rollback would return automakers to pre-recession policies that led to the near-collapse of the domestic industry.

Sens. Ed Markey of Massachusetts, Tom Carper of Delaware and Jeff Merkley of Oregon held a call with reporters Tuesday reacting to media reports that the Trump administration could announce a decision to relax fuel standards put in place five years ago.

Before President Obama left office, the U.S. Environmental Protection Agency said it would leave in place rules requiring the nation’s fleet of light-duty vehicles to rise from the current 34.1 miles per gallon to an average 54.5 mile per gallon standard by the 2025 model year.

The rule came despite automakers' protests that it is unrealistic given the state of technology and consumer demand.

But Markey and others argue that efforts to increase fuel mileage in new vehicles — especially under the agreement reached in 2011 between automakers, federal agencies and California state officials, which have long insisted on tougher standards — was perhaps the “single largest step America has ever taken to reduce climate pollution.” It reduced millions of tons of carbon emissions, they say.

Those supporting the current rule say that while relaxing future standards might give automakers leeway to sell larger vehicles that are more profitable, it also could return the nation to the gas guzzler era before gas prices shot up.

“Making this U-turn on fuel economy is the wrong way to go,” Markey said.

“The carmakers' claim the clean-car standard will hurt industry profits and jobs. … Those are alternative facts,” said Dan Becker, director of Safe Climate Campaign, a Washington, D.C.-based environmental advocacy group. While agreeing with automakers that only a relatively small number of cars currently meet the standards, he said the technology is still there to be more widely introduced with years to go.

“The automakers agreed to these standards. … They were key architects of them,” said Ken Kimmell, president of the Union of Concerned Scientists. “They’re working.”